Mobile phones with digital cameras have long become ubiquitous. In 2014, worldwide smartphone sales surpassed, for the first time, one billion units. According to market statistics and forecasts, by 2018, annual smartphone shipments are expected to grow to 1.87 billion units. Over 80% of all mobile phones will be arriving to customers with embedded digital cameras. This will drive annual sales of phone cameras by worldwide vendors to mobile phone manufacturers, with the purpose of embedding the cameras into smartphones and feature phones, to 1.5 billion units.
Market research indicates that photographing with phone cameras has been the most popular activity of smartphone owners for many years in a row. Recent polls have shown that 82% of smartphone users are taking digital photographs, which exceeds the second most popular application, texting, which is used by 80% of smartphone owners. Market studies also revealed that about 27% of all photographs taken within a year have been captured with smartphones; additionally, the total count of images posted on social photo-sharing sites and taken with smartphones has exceeded the cumulative count for photographs taken with any type of non-smartphone equipment.
Hundreds of millions smartphone users are utilizing smartphone cameras in their business offices and homes. Because paper documents retain a significant role in the everyday information flow of both business users and households, the volumes of digitizing and capturing of paper based information with smartphone cameras are constantly increasing. This trend is facilitated in part by the arrival and advancements in multi-platform content management systems, such as the Evernote service and software developed by Evernote Corporation of Redwood City, Calif. Pages from books and magazines, printed newspaper articles, receipts, invoices, checks, tax and other forms, printed reports, business cards, handwritten notes and memos taken on legal pads, in specialized Moleskine notebooks, on sticky notes or easels, and other types of printed and handwritten documents are benefiting from digital capturing and storage in Evernote where advanced image search and various methods of organization of content items with embedded and attached images are available.
Specialized standalone and embedded applications have been developed, including Scannable software by Evernote Corporation and integrated Page Camera feature in the Evernote software, that may identify and automatically capture document pages from complex scenes, overcoming perspective and other types of image distortion, taking care of poor lighting conditions, varying camera view angles and other challenging circumstances. Advanced methods for robust retrieval of page boundaries provide a solid basis for subsequent image correction and processing.
Notwithstanding significant progress in pre-processing, correction and recognition of scenes captured with smartphone cameras, reliable detection of key parameters of captured documents, such as identification of base page formats from camera phone photographs, still present challenging tasks. In addition to a broad variety of available and standardized page formats in documents, such as ISO 216 and ANSI paper sizes, A-B-C series of page formats with national extensions, letter, ledger, legal, architectural and other specialized formats, there exists a spectrum of additional paper formats used in checks, receipts, stickers, cards, etc. Accurate identification of page aspect ratios from photographs may be further complicated by varying camera view angles and by different focal lengths of phone cameras, as well as by obstruction of page images by other objects in a scene, by damaged page images with uneven page borders (for example, when a user attempts to manually separate two checks from each other in a long band), and by other challenging characteristics of a capturing environment and process.
Accordingly, it is desirable to develop efficient methods and systems for detecting page aspect ratios on photographs of paper documents taken with smartphone cameras.